Diarrhoea and other gastrointestinal troubles caused by pathogenic microorganisms constitute a widespread health problem, which affects in particular tourists travelling abroad, people having received cancer therapy involving antibiotics or radiation, and people working in day nurseries. Such pathogenic intestinal bacteria causing diarrhoea include Salmonella, Shigella, Yersinia, E. coli, Pseudomonas, Clostridium dificile and sordelli, Stafylococcus aureus and Campylobactus. These pathogenic microorganisms adhere to the mucous membranes of the intestine and upset the intestinal function, thereby causing diarrhoea.
It is well-known that microorganisms affect each other positively or negatively by promoting or restraining each other's growth. This interference phenomenon has above all been studied in the flora of the skin, the pharynx and the intestine of human beings. Although the underlying causes are not fully known, it has been found that the normal bacterial flora is of considerable importance in the defence against pathogenic bacteria. The bacteria of the normal flora inhibit invading bacteria in many different ways, e.g. by producing antibiotic-like substances called bacteriocines. Unlike antibiotics, the bacteriocines mostly have a very selective effect on a specific group of bacteria without influencing the remaining bacterial flora. Treating infected patients with such harmless bacteria of specific effect has been not only discussed, but also tried to some extent. Naturally, the bacteria supplied must be able to settle in the intestinal area where they are to produce their effect. This is one of the ideas behind giving soured milk to patients whose intestinal flora is disturbed, and who suffer from severe diarrhoea after treatment with antibiotics. However, there has been no scientific follow-up of what actually happens with the intestinal flora, and the effect, if any, has mostly been uncertain, probably because no bacterial colonisation has taken place in the intestine or because the bacteria supplied lack the capacity to affect the diarrhoea-inducing bacteria. Efforts have also been made to replace the existing bacterial flora in the nasal mucous membrane, the skin and the pharynx with harmless microorganisms, and it has been shown that so-called recolonisation is possible and may be effective.
As mentioned above, supplying bacteria to patients suffering from different illnesses induced by pathogenic microorganisms has mostly been inconclusive, obviously because of insufficient knowledge of what bacteria strains are best suited for bringing about colonisation and interference.
By working under given conditions, it has in recent years been possible to establish important principles for the mechanisms controlling the interaction between different microorganisms, and also to develop methods for examining this interaction. Thus, it has become possible to intervene in this interaction in a meaningful and reproducible fashion, which may be used therapeutically/prophylactically when treating infections.